Coupled polybutadiene is often desired as an additive or to make other polymeric systems such as, for example, high impact polystyrene (HIPS) or acrylonitrile butadiene styrene (ABS) polymers. Typical processes for making such coupled polybutadiene usually involve the use of a halide-containing compound. For example, as described in WO2001/70821, multihalide coupling agents such as a silicon, tin, lead, or germanium multihalide are employed. EP 0019100 describes the use of a gel inhibitor which includes hydrocarbyl halides and silicon halides, as well as, the use of multihalide coupling agents. Unfortunately, the use of such multihalide coupling agents or halide-containing gel inhibitors often results in a coupled polybutadiene which contains residual halide ions. Such halide ions, particularly chloride ions, may facilitate corrosion in the reactors, tanks, and recovery equipment used to produce the coupled polybutadiene and/or any further polymeric systems. In addition, the resulting coupled polybutadiene may also comprise high levels of gels which further contribute to equipment corrosion and/or fouling.
Various approaches have been attempted to reduce or eliminate the equipment corrosion and fouling problems. For example, special steel and protective coatings have been used as described in JP 51007696. Also, basic additives have been employed as described in EP 1217009 and JP10025313. Unfortunately, such approaches are not cost-efficient as they involve more expensive equipment or additives.
Other ways of producing coupled polybutadiene that do not involve the use of a multihalide coupling agent or halide-containing gel inhibitor have also proven problematic. For example, WO2000/073381, JP2001/089543, and JP07002958 employ non-halide coupling agents. Unfortunately, WO2000/073381 and JP2001/089543 each produce a coupled polybutadiene with a high vinyl content (30-60% in the case of WO2000/073381 and 50% in the case of JP2001/089543) while JP07002958 produces a coupled polymer that has three specified molecular weights.
Accordingly, it would be desirable to discover an improved coupled interpolmer such as coupled polybutadiene and process for producing it and subsequent polymers made therefrom which lessened the problem of equipment corrosion and/or fouling. It would further be desirable if such coupled interpolymer composition and process was cost-efficient and produced a coupled interpolymer with a lower vinyl content and more acceptable molecular weight distribution than the processes described above. It would further be desirable if such an improved coupled interpolymer could be useful in making such items as high impact polystyrene and acrylonitrile butadiene styrene.
Advantageously, compositions and processes have been discovered that meet many of the aforementioned needs and also have other desirable characteristics. In one embodiment, the inventive composition is a coupled interpolymer comprising one or more monomeric units derived from a diene wherein the coupled interpolymer is characterized by: a halide content of less than about 30 ppm based on the total weight of the coupled interpolymer; a molecular weight distribution of from about 1.6 to about 2.4; and a vinyl content of from about 5 to about 15 weight percent based on the total weight of the coupled interpolymer. In another embodiment, the coupled interpolymer is coupled polybutadiene, preferably low-cis coupled polybutadiene.
In another embodiment, the inventive process for preparing a coupled interpolymer composition comprising one or more monomeric units derived from a diene comprises polymerizing a diene monomer in the presence of an initiator to form an interpolymer and coupling said interpolymer in the presence of a tetraalkoxysilane. This produces a coupled interpolymer. The coupled interpolymer is often characterized by: a halide content of less than about 30 ppm based on the total weight of the coupled interpolymer; a molecular weight distribution of from about 1.6 to about 2.4; and a vinyl content of from about 5 to about 15 weight percent based on the total weight of the coupled interpolymer. Advantageously, in one embodiment the process may be conducted in the substantial absence of halide-containing compounds.
In other embodiments, the invention pertains to a high impact polystyrene or an acrylonitrile butadiene styrene polymer. Each may be derived from the aforementioned coupled interpolymer such as coupled polybutadiene or more preferably coupled low-cis polybutadiene.